1. Field of the Invention
The present invention relates in general to an adjustable head structure for wrenches having a head unit integrally formed with or separately formed from a wrench handle and, more particularly, to a structural improvement in such a head unit for commonly using the head unit for tightening or loosening nuts and bolts of different sizes by detachably fitting a size adjusting block in the head unit.
2. Description of the Prior Art
In typical wrenches used for tightening and loosening nuts and bolts, a grip opening formed between the jaws of a wrench head has a fixed grip size. Therefore, the typical wrench has a problem in that several wrenches having different grip sizes must be prepared to selectively use the wrenches for tightening or loosening nuts and bolts having different sizes. As these several wrenches having different sizes must be prepared as described above, the wrenches may be lost forcing the owner to purchase new ones.
In order to rectify the above problem of the wrenches having fixed grip sizes, U.S. Pat. No. 2,500,835 discloses a ratchet wrench which is shown in the accompanying drawing, FIG. 1. As shown in the drawing, the head 1 of the above wrench has a ratchet 3 which is biased by a torsion spring 2. In addition, a rotary head unit 6 is rotatably mounted in the wrench head 1. The above head unit 6 is toothed on its outer surface thereby forming a ratchet gear 4. The center of the above unit 6 is provided with a grip opening 5 having a fixed size. The ratchet gear 4 engages with the ratchet 3. The above U.S. ratchet wrench is somewhat preferably used for tightening or loosening a nut or bolt while rotating the head unit 6 in a forward or reverse direction in accordance with the ratchet direction. However, as the above ratchet wrench has a fixed grip size, it is impossible to commonly use the ratchet wrench for tightening or loosening nuts and bolts having different sizes.
On the other hand, Korean U.M. Publication Nos. 85-1175 and 86-3147 disclose adjustable socket wrenches which can be commonly used for tightening or loosening nuts and bolts having different sizes. In each of the above adjustable socket wrenches, the wrench head has an adjustable grip opening whose size can be adjusted by moving a movable jaw relative to a fixed jaw. The movement of the movable jaw relative to the fixed jaw is performed by the turning motion of an adjusting worm. However, it has been noted that the above adjustable socket wrenches have the following problems. That is, as the size of the grip opening of each of the above socket wrenches is adjusted by the turning motion of the adjusting worm, the adjusting worm may be abraded or broken due to the pressure repeatedly applied thereto whenever tightening or loosening nuts and bolts. In addition, the adjusting worm has to be turned in order to adjust the size of the adjustable grip opening according to the size of a bolt or nut whenever tightening or loosening nuts and bolts having different sizes. Therefore, the operational efficiency of the above Korean wrenches is reduced. The construction of above adjustable socket wrench is complicated thereby increasing the cost. Another problem of the above socket wrench is resided in that the adjustable size of the grip opening is limited to a predetermined range.